Austrian police say they have arrested a 48-year-old Ukrainian oligarch who has long been wanted by U.S. authorities on suspicion of bribery and criminal conspiracy.
The man was identified by Austrian government sources as Dmytro Firtash.
He was taken into custody on the evening of March 12 in Vienna without incident.
Viennese police spokesman Mario Hejl confirmed the arrest of a Ukrainian businessman named "Dmytro F.," but said police are not permitted to reveal his last name.
"He is in the hands of the Austrian judiciary, in Vienna, in a relevant detention center," Hejl said. "The rest will be decided by justice."
Hejl added that the detainee was arrested on the basis of a request from Washington.
"We carried out this arrest for U.S. authorities," he said.
A Ukrainian Foreign Ministry spokesman said Ukraine's embassy in Vienna had confirmed Firtash was arrested at the FBI's request.
He had been under investigation since 2006 by the FBI and is being held in Vienna pending extradition proceedings.
Comment from the FBI or other U.S. officials was not immediately available.
Firtash was not listed by the European Union last week among an original group of Ukrainians accused of misusing state funds and violating human rights during the Euromaidan antigovernment protests in Kyiv.
Individuals named on that list had their assets frozen in a number of EU countries, including Austria.
Firtash is one of Ukraine's richest men and has close links to Russia.
He made his money in the gas, chemicals, media, and banking sectors and was a key backer of recently ousted Ukrainian President Viktor Yanukovych.
Firtash was one of the owners of RosUkrEnergo, a gas-trading company that served as the intermediary in gas dealings between Russia and Ukraine.
He also controls much of the titanium business in Ukraine.
Firtash is considered to be one of the leading investors in energy and chemicals in Eastern Europe.
Within his Group DF company, he has business assets in Ukraine, Estonia, Tajikistan, Germany, Italy, Cyprus, Switzerland, Hungary, and Austria.
Firtash was alleged to have given financial support to the political party of Ukrainian opposition leader Vitali Klitschko, a charge the former world boxing champion denied.
Former Ukrainian Prime Minster Yulia Tymoshenko filed a lawsuit against Firtash and RosUkrEnergo in a New York court for "defauding Ukraine's citizenry by manipulating an arbitration hearing," a reference to a 2010 international arbitration ruling in Stockholm that ordered Ukrainian state energy company Naftogaz to pay RosUkrEnergo billions of dollars worth of oil.
Firtash has also been accused of being involved in the jailing of Tymoshenko, who was released from prison last month.
With reporting by RFE/RL's Claire Bigg, Reuters, ITAR-TASS, AFP, and AP